Obstructive sleep apnea is a condition in which the patient's airway passage is blocked and no air can pass to the lungs during sleep. During a customary sleep period a person suffering from sleep apnea can experience so-called apneic events. Apneic events are periods when the patient's airway becomes blocked, often for ten seconds or more, until the patient rouses from sleep and starts breathing normally again. Those suffering from sleep apnea may experience numerous apneatic events each night, causing a deficiency of restful sleep and, due to depleted oxygen levels, possible long term health problems such as heart ailments.
Continuous positive airway pressure (CPAP) and, more specifically, nasal continuous positive airway pressure (nCPAP) has been shown to be an effective treatment for sleep apnea. See "Benefit of Nasal CPAP in Obstructive Sleep Apnea is Due to Positive Pharyngeal Pressure", N. C. Abbey, K. R. Cooper and J. A. Kwentus, Sleep 1989, 12 (5):420-422; "The Effect of Nightly Nasal CPAP Treatment on Underlying Obstructive Sleep Apnea and Pharyngeal Size", N. A. Collopp. A. J. Block and D. Hellard, Chest 1991, 99:855-860; and "Nasal Continuous Positive Airway Pressure Facilitates Respiratory Muscle Function During Sleep in Severe Chronic Obstructive Pulmonary Disease", B. J. Petrof, R. J. Kimoff, R. D. Levy, M. G. Cosoi and S. B. Gottfried, Am. Rev. Respir. Dis. 1991; 143:928-935. This treatment involves applying a constant supply of gas, typically a mixture of air supplemented with moisture vapor or oxygen, to the nasal passages at a predetermined, slightly elevated pressure in order to prevent negative pressure conditions within the passageway.
More recently, a related form of treatment has been tested and may achieve success similar to nCPAP. In this treatment, known as BiPAP.TM. therapy, a controller regulates the gas pressure in response to the patient's breathing patterns and supplies positive gas pressure at a first gas pressure during the inspiratory phase, i.e., inhalation by the patient, and supplies gas at a second, reduced pressure during the expiratory phase, i.e., as the patient exhales. The first gas pressure typically corresponds to pressure used in nCPAP treatment, and is on the order of about 10 centimeters of water or greater. The second pressure level is about half the first gas pressure, and typically is about 5 to 7 centimeters of water pressure. It has been reported that reducing the gas pressure during exhalation provides increased patient comfort and compliance by reducing the work done by the patient in overcoming the gas pressure during exhalation. BiPAP.TM. treatment is disclosed in "Obstructive Sleep Apnea Treated by Independently Adjusted Inspiratory and Expiratory Positive Airway Pressures via Nasal Mask", M. H. Sanders and N. Kern, Chest 1990; 98:317-24; "Nocturnal Nasal Intermittent Positive Pressure Ventilation with Bi-level Positive Airway Pressure (BiPAP) in Respiratory Failure", R. E. Waldhorn, Chest 1992, 101:16-521; "Efficacy of Nocturnal Nasal in Patients with Restrictive Thoracic Disease", Am. Rev. Respir. Disease, 1992; 145:365-371; "Physiologic Evaluation of Pressure Support Ventilation by nasal mask in Patients With Stable COPD", N. Ambrosino, S. Nava, P Bertone, C. Frachia, C. Rampulla, Chest 1992; 101: 385-91. As will be appreciated, BiPAP.TM. treatment requires sensing and control mechanisms to monitor and adjust treatment gas pressure.
In general, nCPAP and BiPAP.TM. treatment typically involve placing a mask over the nose of the patient by means of a harness or other headgear and providing a source of positive low pressure air connected to the mask. One such mask is the Sullivan Bubble Mask, available from ResCare, Inc., San Diego, Calif.
U.S. Pat. No. 4,782,832 issued to Trimble, et. al. proposes a device for nCPAP treatment intended as an alternative to conventional mask devices. The Trimble structure has become the accepted apparatus for nCPAP treatment. Trimble discloses a nasal puff adapted to be worn adjacent the nose of the wearer-patient. The nasal device includes a relatively small plenum chamber including structure defining an inlet adapted for coupling with a source of gas, and a pair of spaced apart, separate gas outlets in communication with the inlet. Typically, the plenum chamber is in the form of a generally Y-shaped hollow body with the gas outlets located in the branches of the body. The nasal puff further includes a pair of gas delivery elements each having a gas flow passageway therethrough and respectively operatively coupled with a corresponding gas outlet for conveying gas from the outlet through and out the passageway. Each of the gas delivery elements is configured for insertion into a respective naris of a patient, and for this purpose the outer wall of the elements are generally frustoconically shaped so as to sealingly engage the naris-defining surfaces of the nose. Adjustability of the naris elements is provided by rotatably mounting the elements to the plenum housing and by mounting the elements in slots permitting selective lateral positioning of the elements with respect to each other. Flexible bellows-type corrugated sections can be provided in each of the elements and/or in appropriate positions in the plenum housing so as to add further ranges of flexibility and adjustability. The nares elements are fabricated from relatively soft, deformable, shape-retaining synthetic resin material permitting manual deformation and alteration of the effective shape and position of the elements. Trimble discloses a harness to be worn on a patient's head with flexible retaining straps extending from the main harness strap to each side of the nasal puff. The harness assembly includes an elongated gas-conveying tube which is adapted for coupling with the inlet of the nasal puff and extends upwardly along the length of the bridge of the patient's nose and across the patient's forehead, terminating at the top of the patient's forehead. The tube is longitudinally bifurcated to divide the overall tube and present a pair of elongated, juxtaposed passageways, one of which is connected to a source of pressurized air and the other to a discharge tube for purging patient-generated CO.sub.2 during exhalation). In an alternative embodiment Trimble discloses inflatable nares elements that are inserted into the nares and inflated manually by a separate source of pressure.
The Trimble nasal puff and harness assembly is an accepted apparatus for treatment of sleep apnea using nCPAP therapy. While the Trimble device is an improvement over prior mask structures, some patients continue to object to the Trimble structure as uncomfortable to wear. Studies show that a small but significant number of patients fail or are unable to continue nCPAP treatment due in at least some cases to the inconvenience or discomfort of wearing the presently available apparatus. See "The Effect of Positive Reinforcement on Hourly Compliance in Nasal Continuous Positive Airway Pressure Users with Obstructive Sleep Apnea", E. C. Fletcher and R. A. Luckett, Am. Rev. Respir. Dis. 1991; 143:936-941; "Maxillofacial Surgery and Nasal CPAP", R. W. Riley, N. B. Powell, C. Guilleminault, Chest 1990; 98:1421-1425; and "Surgical Treatment of Obstructive Sleep Apnea--Is Mandibular Surgery an Advance?", Chest 1990; 98:1315-1316.
U.S. Pat. No. 5,269,296 to Landis discloses and claims a nasal airway pressure device having a pair of cannulae. Each cannula has an inflatable cuff in gaseous communication with the cannula lumen such that the cuff is inflated during use to gently but securely position the cannula relative to the sensitive nares walls. The Landis 296 patent also discloses vent holes adjacent the cannulae for relieving excess gas pressure created during exhalation.
U.S. Pat. No. 5,477,852 to Landis and Disanza discloses and claims a nasal airway pressure device including a variable orifice vent hole.
A mask having a valve is proposed in Rapoport U.S. Pat. Nos. 4,655,213 and 5,065,756. A mask with a flap valve is shown in Bolton U.S. Pat. No. 1,158,780.
Notwithstanding the general consensus that nasal positive airway pressure is an effective treatment for sleep apnea, a substantial number of patients either cannot tolerate treatment or choose to forego treatment. It is believed a substantial number of such patients could benefit from a nasal positive airway pressure apparatus which is more convenient to use and comfortable to wear, thereby resulting in increased treatment compliance. The device disclosed and claimed herein may find application to either nCPAP or BiPAP treatment.